Both Camera Raw 5 and Lightroom 2 support the PowerShot SX1 IS. However, ACR and Lr ignore the DPOF (Digital Print Order Format) information. The DPOF information is saved in the MISC directory of a storage device and this information can then be used to print directly to a DPOF compliant printer.
See Summary of DPOF Version 1.10 for more information.
Thanks for the response.
I've done a bit more research and have begun to suspect there is an underlying difference between our normal use of "File Format" and that of the manufacturer. It appears that for a few more bucks I can upgrade to the SX1 IS which supports "Image Compression of Normal, Fine, SuperFine, RAW", at lower megapixels (10 vs 12), as opposed to the SX20 IS which supports only Normal and Fine.
I'm led to conclude that from our point of view the underlying File Format is likely, JPEG.
From my point of view its easier to understand DPOF as some sort of exchange protocol, rather than an image file format.
As much as I hate to physically go to the Mall, I guess I'll have to to settle the point.